Light emitting devices that combine a semiconductor light emitting element with a phosphor have received interest as next-generation light emitting devices holding the promise of low power consumption, compactness, high luminance and a wide range of color reproducibility, and they are being actively researched and developed. As such phosphors, oxynitride phosphors, which have oxynitrides as a base material and are activated by transition metals or rare earth metals, are widely used for having good light emission properties, thermal stability and chemical stability. As phosphors that are representative of oxynitride phosphors, β-sialon phosphors, α-sialon phosphors and the like are known, and have come into wide practical use.
In order to improve the color rendering and luminance of such light emitting devices, various attempts have been made to improve the light emission properties of oxynitride phosphors.
For example, in consideration of the fact that conventional green and yellow phosphors have low light emission efficiency and are not capable of achieving high-luminance light emissions, Patent Document 1 proposes to limit the composition of an oxynitride phosphor to a specific range, and to construct a chemically stable base structure having sites where Ce or Eu atoms can be easily substituted, thereby obtaining a phosphor that has a wide and flat excitation band, a broad light emission spectrum, and also excellent light emission efficiency.
Additionally, Patent Document 2 describes that a wide range of emitted colors can be obtained, and the crystallinity and light emission efficiency can be improved, by changing the elements and composition ratios contained in oxynitride phosphors.
Furthermore, Patent Document 3 describes that the temperature properties and light emission efficiency can be improved by limiting the composition of an oxynitride phosphor to a specific range.